An apparatus for flattening the upper edges of a pouch or packet preparatory to sealing is disclosed in U.S. Pat. No. 2,913,862 wherein the pouches while traveling along a predetermined path at a predetermined speed are flattened by mechanism which includes a pair of jaws which clamp the trailing ends of the pouches and a pair of coacting gripping rolls which grip the leading ends. The jaws which clamp the trailing ends move at the same speed as the conveyor carrying the pouches along the path of movement and the coacting gripping rolls rotate at a faster rate than the conveyor to pull the leading ends of the pouches forwardly relative to the fixed trailing ends of the pouches thus to flatten the upper edges. Since the body portions of the pouches are confined, pulling the leading ends at the mouths forwardly tends to stretch and produce diagonal distortion of the pouches. The apparatus as herein disclosed is designed to effect straightening of the edge portions without distortion and further to hold the straightened edge portions once they have been straightened intimately engaged until sealed and to heating the edge portions to render them adhesive for sealing without damaging the edge portions or the body portions therebelow.